6. Snowball earth

Question 1

What was/is ‘snowball Earth’?

Answer 1

A series of glaciations in the Neoproterozoic period in which it is believed the entire Earth may have been covered in Ice

Question 2

When was the Neoproterozoic period?

Answer 2

Last era of the Proterozoic (and Precambrian)
- 1000-542Ma

Question 3

What are some examples of glaciation evidence on/in rock?

Answer 3

Glacial diamictites, ice-scratched surfaces (striation etc), dropstones

Question 4

What is a runaway effect?

Answer 4

A positive feedback loop in which a situation ‘worsens’ itself

Question 5

Describe the ice albedo process.

Answer 5

• Begins with polar ice caps
• These are highly reflective and reflect rays back into space
• More ice = more reflection
• Positive feedback loop where more ice lowers Earth’s temp

Question 6

What is the best theory for why snowball Earth stopped?

Answer 6

A decrease in silicate weathering (allowing CO2 to build up again and warm the Earth)

Question 7

What is the process widely believed to be the cause of snowball Earth?

Answer 7

Ice Albedo process

Question 8

Describe how a decrease in silicate weathering can raise Earth’s temperature.

Answer 8

Less carbon dioxide would be removed from the atmosphere, while volcanic output would continue - so more CO2 builds up and causes global warming.

Question 9

Why would snowball Earth have caused a decrease in rates of silicate weathering?

Answer 9

Less rock is exposed due to ice cover, and rates slow anyway when temperatures drop

Question 10

What sort of timescale did the melting of snowball earth occur on?

Answer 10

Thousands not millions of years

Question 11

What atmospheric conditions followed the melting of Snowball Earth? Why?

Answer 11

A super greenhouse effect and period of intense weathering because carbon levels had increased

Question 12

What evidence is there for a period of super greenhouse effect after snowball Earth?

Answer 12

Thick limestones over glacial deposits which are warm water sediments

Question 13

What less substantiated evidence is there for snowball Earth?

Answer 13

• Return of BIFs, possibly due to ice cover preventing photosynthesis
• Lower delta13-Carbon levels, suggesting less use of delta12-C by sea life

Question 14

What is a possible theory for the cause of snowball earth involving life?

Answer 14

Lichen eating/dissolving continental rocks (drawing down CO2 and increasing silicate weathering), and mobilising nutrients to sea causing an algae bloom.

Question 15

Does increased silicate weathering cause an increase or decrease in CO2?

Answer 15

Decrease

Question 16

What major period/event follows snowball Earth? (by a few million years)

Answer 16

Cambrian explosion

Question 17

What is the significance of carbonate fragments in high latitude diamictite groups?

Answer 17

This suggests these groups moved over carbonates/were bounded by them - these being carbonates only known to form below 30°. Suggesting some high latitude glacial evidence is really from the equator.

Question 18

Is a higher latitude closer to the equator or the poles?

Answer 18

Poles. Latitude is 0 at the equator